Suspension device for vehicles



Jan. 9, 1951 P. w. THORNHILL 2,537,491

SUSPENSION DEVICE FOR VEHICLES 2 Sheets-Sheet 1 Filed Sept. 21, 1944 Jan. 9, 1951 P. w. THORNHILL 2,537,491

SUSPENSION DEVICE FOR VEHICLES Filed Sept. 21, 1944 2 Sheets-Sheet 2 Patented Jan. 9, 1951 SUSPENSION DEVICE FOR VEHICLES Peter Warborn Thornhill, Leamington Spa, England, assignor to Levitation Limited 4 Application September 21, 1944, Serial No. 555,150 In Great Britain September 2, 1943 13 Claims.

This invention. relates to suspension devices for vehicles and especially to those of the kind in which the static load is supported in a resilient manner by a quantity of compressed gas, the device having a working space, the volume of which varies as the position of the wheel or equivalent changes with respect to the vehicle body or equivalent, variation in the volume of the working chamber being arranged to cause the pressure of the compressed gas to change. Suspension devices of this form are already known in which the variable volume working space is largely occupied by gas under pressure, the arrangement shown in British Specification No. 450,852 being an example. In this prior arrangement a compressed gas chamber of constant volume communicates with the working space by way of a double-acting valve, the operation of which latter is controlled by a further quantity of compressed gas disposed within an auxiliary chamber and having a very constricted means of communication with the main gas chamber.

It'is an object of the invention to provide an improved, compact and relatively simple form of suspension unit in which air or other gas is used in a particularly efficient manner both as a resilient medium and as a means for damping the movement of the device. It is a further object of the invention to provide an improved form of telescopic suspension unit which is particularly adapted for use in connection with motor road vehicles.

According to the invention a suspension device for a vehicle comprises a pair of relatively movable elements for attachment to the vehicle body or equivalent and to the vehicle wheel or equivalent, respectively, said elements defining a first variable volume space containing gas under pressure, a second gas space the volume of which changes at the same time as, but in the opposite sense to, the volume of the first variable volume space, a damping valve adapted to connect said two variable volume working spaces, and an auxiliary chamber having a constricted communication with the first variable volume space and bounded by a control piston, which latter is acted upon by gas within the auxiliary chamber, and regulates the passage of gas through the damping valve during recoil movements of the elements.

The invention is illustrated by way of example in the accompanying diagrammatic drawings, in which:

Figure 1 is a side elevation of a typical telescopic suspension device, the cylinder being shown in section;

Figure 2 is a fragmentary longitudinal section of the piston head and part of the plunger, the valve being shown in the position which it occupies during shortening of the device and the figure being drawn to an enlarged scale;

Figure 3 is a similar View showing an operative position of the damping valve during the progress of the following recoil extension stroke; and

Figures 4, 5, 6 and '7 are similar views showing modifiedconstructions of damping valve.

The suspension device shown in Figure 1 comprises a tubular cylinder III, which is closed at its upper end by a cap ll having an integral lug l2 by which the upper end of the device is adapted to be secured to the body or equivalent of the vehicle (not shown). A plunger mem ber, indicated generally at I3, is slidable within the cylinder [0 and comprises a stem portion [4, which is conveniently tubular so as to save weight and is slidable through a packing gland l5 of any suitable constructioncarried by the lower end of the cylinder H). The external diameter of the stem i4 is substantially smaller than that of the bore it of the cylinder I0, thus leaving an annular working space l8, which is herein referred to as the second variable volume working space. It is separated from what *is termed the first variable volume working space ll at the upper part of the cylinder [0 by a piston head H], which latter fits slidably in the bore I6 and is provided with a packing ring 20 engaging said bore in a substantially fluid-tight manner. At its lower end the stem [4 is provided with a lug 2| by which the device is attached to a wheel axle or equivalent, and for convenience in manufacturethe lug 2i is formed with an axial spigot 22, which fits into the lower end of the stem M and is held in position by an axial tension rod 23; the upper end of the tension rod 23 is screw-threaded into a downward extension 24 of the piston head H), as indicated at 25. An axially extensible tubular boot 26 has its ends secured respectively to the cylinder at 27 and to the plunger member I3 at 28 for the purpose of excluding dirt and other foreign matter from the external sliding surface of the stem 4. The first and second variable volume working spaces 11 and I8 are charged with air or other gas under pressure through an air inlet valve 29 conveniently fitted in the cap ll of the cylinder; it should be noted that in the suspension devices which are described herein the'working spaces I! and I8 have no means of communication with the interior of the plunger stem I4, and this stem functionsas, and can be regarded as, a. solid rod. Communication between the first variable volume working space H and the second variable volume working space |8, through the piston head i9, is controlled by a damping valve, which is indicated generally at 30; passages 3| lead from the damping valve 30 into the Working space 18.

The preferred form of damping valve is shown in Figures 2 and 3, and comprises a control piston 32, which is slidable in a substantially liquidtight manner within a bore 33 forming a control cylinder in the piston head Hi. The control piston 32 is of a hollow construction and is fitted at its upper end with a bush 34 having a constricted passage 35 communicating at all times with the first variable volume working space H. Attached to the bush 3 is a tube 35, the lower end of which is in communication with a chamber 3! formed partly within the control piston 32 and partly within the lower end of the bore 33, which latter is closed by an end wall 38. The chamber 3'1 is herein termed the control chamber, and owing to the provision of the constriction 35, gas pressure in said chamber 31 when the device is in a stable condition tends to become equal to the gas pressure in the first variable volume space l1. Leakage from the control chamber 37 around the outside of the control piston 32 is prevented by the provision of an annular packing ring 39 within a groove in said control piston. Adjacent its upper part the control piston 32 is formed with an annular groove 40, which is in permanent communication witha number of radial passages 4| the groove 49 and passages 4| together constitute what is herein termed the transfer passage. The passages 4| lead into the inner curved surface or bottom of a circumferential groove 42 formed in the Distonhead' IQ for the accommodation of the packing ring 20. This packing ring comprises an outer annulus 43 of soft material such as rubber or rubberised canvas, and an inner ring 44 which is composed of metal and is arranged to spring outwards so as to hold the outer ring 43 infirm engagement with the bore IG of the cylinder. It will be noted that the axial measurement of the packing ring 28 issubstantially less than the corresponding width of the groove 42, and this enables the packing ring 20 to function as the combined valve member of a dual nonreturn valve device, controlling the flow of gas between the transfer passage 4|], 4| and the first and second variable volume spaces I? and I8. Substantial clearance is provided between the bore 16 and the outside of the piston head l9 so as to enable fluid to fiow from either of the working spaces ii and I8 into the groove 42, or axial passages or grooves may be formed in the piston head for this purpose. It will be seen that when the plunger 13 is moving upwards, pressure fluid tends to fiow from the Working space H to the working space IS. The packing ring 20 tends to be left behind, as shown in Figure 2, due to the frictionbetween it and the cylinder bore l6, and prevents said fluid from passing into the space I8; it can flow freely, however, into the transfer passage in, 4|. The packing ring 20 is also urged towards the bottom of the groove by the superior gas pressure in the working space Conversely when the plunger I3 is moving downwards, a superior pressure exists in the working space |8, the packing ring 22! being lifted so as to bear against the upper side wall of the groove 42, thus sealingrthe transfer passage 46, 4| from the working space H and placing it in free communication with the Working space l8.

lit)

The passages 3| in the piston head l9 lead to a series of ports 45 in the bore 33 at a position below the passages 4|, the arrangement being such that when the control piston 32 falls to its retracted position shown in Figure 2, the groove 46 connects together the passages 4| and 3|, said passages 4| then being isolated from direct communication with the first variable volume space I! by th engagement of the upper land 46 of the control piston 32 within the upper extremity of the bore 33. In a similar manner, when the control piston 32 rises to its extended position, as

shown in Figure 3, its outer cylindrical surface 41 below the groove 40 shuts off the passages 3| from the transfer passage 40, 4|, and at the same time the land Mi rises above the upper surface of the piston head l9, consequently placing the transfer passage 40, l into communication with the first variable volume working space ll. The passages 3|, Al and the groove 40 thus act as a change-rover valve actuated by the piston element 32. This piston element '32 has a relatively long free travel, so that although the quantity of air in the control chamber 31 is prevented by the constriction 35' from changing rapidly, the pressure in the auxiliary chamber 3! nevertheless varies in sympathy with the pressure fluctuations in the working space I"! as the plunger |3 freciprocates. The control piston 32 is preferably retained within the bore 33 by a small diameter pin (not shown) fitted to the piston head so as to extend radially into the groove 40 at about the level of the ports 4|. 7

The method or operation of the suspension device is as follows. When the vehicle is travelling along a smooth road or is stationary, and therefore the suspension device is steady, the normal static load is supported by the air pressure within the working space H of the cylinder acting downwards upon the piston head I9 over an area equal to the cross-sectional area of the stem portion M of the plunger l3, for, of course, the annular space |8 between the stem portion l4 and the cylinder l0 contains air under pressure tending to force the piston head is in an upward direction. The constriction 35' of the damping valve 33 causes the pressure of air in the auxiliary chamber 31 to be the same asthat in the cylinder space 81. When the vehicle wheel strikes a bump the suspension device tends to shorten but the resistance to such movement is arranged to be as small. as possible so as to reduce the increase in the upward thrust on the vehicle body. Thus during the upward movement of the plunger member 53 the pressure of the air in the working space tends to increase and therefore presses down-the control piston 32 against the force exerted by the air in the control chamber 31. At the same time the packing ring 29 is forced downwards to the position shown in Figure 2-, partly by the effect of the superior air pressure on its upper surface and partly due to the fact that the piston head I9 is travelling upwards within the cylinder l8, so that the packing ring 20 naturally tends to lag behind due to mechanical friction. The air from the upper space H can therefore flow freely into the passages 4|, the groove 48, and thence into the annular working space l8 by way f the passages 3|. The upward movement of the plunger member l3 of course takes place very rapidly, so that the quantity of air in the control chamber 31 does not vary appreciably. Bythe time that the upward movement of the plunger member 53 is finished, the

air pressure in the working spaces l1: and H! is er course greater thanthe normal static value, and the piston valve member 32 is consequently well depressed; therefore when the downward recoil stroke of the plunger member l3 commences, the control piston 32 remains in its lowered position. Air from the working space I8, however, tries to return to the working space H, but this flow is'prevented owing to the fact that the packing ring 28 rises into engagement with the upper side wall of the groove 42, as is shown in Figure 3. The downward movement of the plunger member I3 therefore takes place against considerable resistance, the air trapped within the annular working space l8 becoming compressed. In the meantime the air pressure in the working space H progressively falls, and the control piston 32 rises'in piston head IQ, so that when the pressure becomes less than its normal static value, 1. e. the pressure at which it is only just able to support the gravitational load on the wheel, the control piston 32 has moved to, say, the position shown in Figure 3. Air from the annular working space it is then able to fiow through the transfer passage ll, 40 and past the edge of the upper land 56 into the upper working space II. This flow, however, is automatically regulated so as to prevent the pressure in the working space i! from rising above its static value, the control piston 32 becoming depressed to close the transfor passage cl, so should there be any tendency for the pressure in the space it to rise above the value of the pressure in the control chamber 3?; It will be noted that when the control piston 32isolates the transfer passage Mi, 4% from the working space II, as shown in Figure 2, it is in a state of balance as far as the air pressure in the transfer passage 45, 40 is concerned and therefore If the pressure in the space ['7 should fall below the static value, however, the control piston 32 during the commencement of the downward recoil stroke the pressure of the air in the lower working space [8 has no effect whatever in moving the control piston 32 to its raised position. The damping valve device has the same efiect when the suspension device is lengthened with respect to its static position, say owing to the wheel dro'pping'into a pothole. The plunger member 53 can move downwards relatively freely, as this tends to reduce the pressure of air in the upper working space H, thus causin the air in theauxiliary chamber 3? to force the control piston 32 to its raised position as shown in Figure 3. Air can therefore escape freely from the annular working space l8, past the lower part of the packing ring 26, and through the transfer passage Lli, 48 into the working space H. During this portion of the movement the weight of thevehicle is not fully supported and the body or equivalent therefore tends to assume a downward momentum. Also the final pressure in the work'- ing spaces i7 and i8 is less than the static value and is therefore less than the pressure of air in the control chamber 37. Consequently the control piston 32 is held in its raised position, so that when the recoil shortening stroke commences, the air within the working space ll becomes compressed, for it is unable to flow past the packing ring 2! the latter then being in engagement with the lower wall of the groove 42. When, however, the pressure in the working space ll becomes greater than the static pressure, the control piston 32 is forced downwards and the parts are then disposed in the positions shown in Figure 2; it will be seen that air from the working space H can flow past the upper part of the packing ring 20 and into the working space l8 by way of the'transfer passage 4|, and the passages 31.

is automatically raised, thus shuttingcff the flow of air until the pressure in the working space I! has again fallen below the static value. A substantial upward thrust is thus maintained upon the cylinder during the shortenin stroke, this thrust being at least equal to the normal staticload and thus being able to bear the gravitational load in such a manner as to neutralise as quickly as possible the downward momentum which was initially acquired by the vehicle body r stantial quantity of oil or other lubricating liquid,

and the control piston 32 is provided with the tube 36 in order to prevent the control chamber:

3'1 from becoming completely filled with such liquid, as of course this would render the damping valve device ineffective. During the telescopic movements of the piston l0 and plunger member i 3 a slight alternating flow of air occurs through the constriction 35; therefore if the liquid should tend to accumulate in the control chamber 31 to a level above the bottom of the tube 36, this liquid will be ejected through said tube whenever the pressure in the control chamber 31 exceeds that in the working space H, whereas when the opposite conditions prevail air from the working space i? will be forced into the control chamber 3i.

It will of course be realised that the lower part of V the combined piston and change-over valve member 32 acts in the manner of a control piston which is subject to the pressure in the auxiliary chamber 3?, and that the working characteristics of the suspension device can be modified by making the area ofthis control piston smaller or greater than the eifective area over which the pressure in the working space H acts upon the control piston 32. It will moreover be understood that the construction of the piston head 19, and more particularly the damping valve device 33 disposed therein, may be varied in numerous ways so as to secure substantially the same effects as those described above.

In the modified construction of damping valve shown in Figure 4 the control chamber 31 is bounded by a control piston 48, which is of inverted cup shape and which fits slidably within the bore.33 just suificiently loosely to allow the air pressure in the. control chamber 37 to become equal to that in the working space It when the suspension device is in a stable condition; the leakage past the control piston 48 is, however, not sufficiently great to bring about substantial changes in the quantity of air in the control chamber 37 as a result of the rapid fluctuations in pressure which occur in the suspension device when the latter is in a state of telescopic oscillation. At its upper part the control piston 48 is formed with a spigot 49 having a nut 5Eiwhich serves to clamp a head'member 5| against a shoulder 52. This head member has at itsupper' and lower parts frusto-conical surfaces 53 and 54 respectively adaptedto engage in a substantially fluid-tight manner with corresponding seatings 55 and 56 at the upper and lower extremities of a circumferential enlargement 51 of the bore 33. The head member 5! is formed with passages 58 extending parallel with its axis, and

constitute what is termed the transfer passage."

Theupper, andflower endsaoix' he.;passa sz& are.

' controlled by ainair:onopnosinganonereturnwaives:

comprising annular: washers: 6.9.; andi Bl; which are adaptedetq .fitdnza fiuid-tighhmanner against. the, upper-andiowerflatsurfacescoir.theheadmember; 51; The washers 60,:and B1! are freeto move. 231815 1y." for. a. short. distance. the washer 611: being slidably' :llpQnx a. spigot: 62-. formed. 011;. the lower: partiof the} nut; 55;. while; the. washer. 8.8. is. slide-- able :upon. the base; portion; of the. spigot 49, and. has-.itstravellimited by a shoulder 6.3. The-axial separation of v the seatingss. 55: and 5B; is. sufficient to allow.- the head; member. 51 freedom. to move axially. for a. substantial. distance; it; follows, therefore, that when the head member-5i iSClOSL ings one oftheseseatings 55: and 5.5;.the other is. open. Surrounding thelower part; of: the spigot; Aihisanannular space ciwhichisin permanent oommunicationwith the passages leading-to. the=annular working space [8. The packingrin mumthiszinstanceista-snug fit within the grooveingthepistonhead l9 and merely servestopre ventrlea-kagez past the outside of. the pistonhead [82 This modificationoperates inthe same. manner. asin the previous: example. The air. pressurewhicheis presentinlthecontrol chamber 31, and whichzisequalto the static pressure of the device, governsithe operation of the change-over valve CQRStitHtBd.bYfthB-hfld member 5 it andthe seatings 55 and 56. Thus during shortening of the device .from: its .static position the control. piston 48a. is; depressed; andiair from the working space H1 flowsrpast the seating 5 5; through. the transfer. passagefi]; 58;.58, and entersathe working space l8zby. opening the nona-returnvalve fit andfiow ingzthrough the passagesfil. During. recoil the headmem'beifi [remains depressed and thus traps the; air within; the working space l3 until suchtimesasrthe pressure withinthe working space IT falls=he1ow the; normal static. value; at: this point the head ,member. 5] raised, thus opening the seating 56. and. enabling. air. from the working: space. l.&;to fiowthro-ugh the transfer. passage and past the Y non-return. valve to. into the working space I! only 'so long-aslthe'zpressure insaid space 111.- does; not: exceed. the. static value. When the device -becomes1.=elongatedbeyond its static lengththereductioninpressurewithinthe working space H; causes. the head-,membenSl to heraised-into engagement-with. the seating.55, so that .aincan; flow. freely from the contracting workingspace [.Bjthltollgh the; passages 3.], pastztheseatingjfil and through; the transfer passage,- past: the. nonreturmvalvetainto the workingspace- I]; At the. commencement of the following shortening or; re coil; stroke the; air; prevented from; returnmg immediately to. the .workingspace iii as-the head member 5 l remains. in engagementwithzthe seata ing;5.5-, since the air; pressure in the controlfchamher- 31 is smaller'than that pret'ailing in..the: working space I]. As aresult the device con.- tinues to shortenuntil; the-pressurev in. the work.- ing; space i! builds upto. a value which; is; in: excess of the statiovalue, whereupon the head member 5|. movesdownwards into engagement 7 82 faces" 68; and; 69:11pm a:.spoolesha edchangeeoven valve: member; 10; which lattenis; conveniently. iormedjntegrally-with.thecontrol piston: 48;. The valve member-.mzhas amaxial' passage H; which.

i; isgeniargedrat its centre: part.and;oontains a.pair;

etral passage 1'! leads fromthe lowerrendofxthea passageli intothe annular. space-69, and thence byrway. of passages-Shinto theannular working? space: I81. As; before,. sufiicient; leakage. of air;- takes-place. around the control piston-482w maine tain in the control chamber- 37 .pressure:which:

isequal to; that: prevailing in the working spaces" IL'a-nd l8lwhen;the. device is bearingits normal. stat-irrloadz. Therefore whenthe suspension. dc.- vice becomes shortened, duetothewheel enconne tering; ahnmothe excessive pressure inthe. work ingzspace-gl '4 causes; thevalve member-wand con.- trolpistoniwto oedepressed; thuslclosingzthe seating. 66 and opening the seating 6-] of the. change-over valve. Air can. then flow freelythrough the. non-return valve '12, the, transfer.

passages 15, I6, past the open seating. 61, into. the: working: space. i8. At. the beginning. of? the following recoilstroke, however; the escape of air. ironnthe; working-space I8.is. prevented; by the:

fact thattheseating remains. closedbythe surface Slheh the valve. memberllfl; whileof course;

the; non-.returnzvalve 12. also prevents-flow oftair. into the'space' 11.. When thepressure ofthe air. in; the working. space I'L falls. below the-static:-

value; however, the control piston 48 ;raisestthe' controhvalve. member solthatair from. the: annularnvorking space i8; can then flowsthrough: the passage. 17;. past: the. nonereturn. valve: 13; through the-transfer-passage I5, 18, and into the space I! by way-of. the seating; 66;. The'reverse action occurswhen the. suspension device. becomes lengthened,l.say due to the wheelcfalling into a; pothole;

In the. arrangement shown inIEigure 6 the controlpistonfiris arranged as a change-overpiston' va lveof'rsubstantiallythe same form as. in Eigures 2; and; 3; The. non-return. valves are, however, fitted intdthe pistonhead lfihandcompriseaipairl ofiballs 12a and'lta; held. apart inaengagement with theiriseatings by a coiled compression spring lean Achamherq? lmhetween-theballs is in per-- manentcommunication hy apassage- Mawith the annnlar'groove. c0: of; the valve member-32 theopenings H a;: Q l a: and: 40 together constituting.

whatisgtermeithe transfer passage; The oper-' ation ofiathe change-over. valve device shown-in. Figure. 6i-is;eXactly. the same asthat in Figures 2.and13;..

Yet another constructional variationis illustratedjn .Eigure 7, .where the :change-ovenvalvets is: again of: the piston type: comprising: a piston; valve-.memher: 32 formedjntegrally with the :conetrol: piston 48;. The non-return;valves,.however,

comprise fiat metal washers 78-) and? 9. which are.

disposedrwithin the annular groove 40 and: are; urged apart by .-a-.coiled compressiorr springrflfll. Ilia-washer. '18 thus? closes a. circular series. of passagesa: formed in the upper: land. 46 ofithe' valve member 32 while. the. washer. l9: similarly:

61.. Thesetare.engageablebm-frusto+eonicahsurcloses-:theupper endsiofja series of=; h=shaped1 passages 82 which are formed in the lower land 41 and are in permanent communication with the annular working space l8 by way of the passages 3!. In this instance the transfer passage is constituted solely by the annular groove 40; otherwise the relationship of the parts and the method of operation is the same as the devices shown in Figures 5 and 6.

What I claim is: a

1; In a pneumatic suspension device for ehicles having a cylinder closed at one end, a plunger of substantially smaller diameter than the cylinder and slidable therein, packing means on the end of the cylinder forming a seal against the plunger, and on the inner end of the plunger a piston head which slidably engages the interior of the cylinder, and divides the interior of the cylinder into a first variable volume space bounded by the piston head and the closed end of the cylinder, and a second variable volume 1 space of annular cross section surrounding the plunger, said first and second variable volume spaces both being charged with gas under pressure, the provision of a pneumatic damping valve system comprising a control cylinder within the plunger. a control piston slidable in the control cylinder to form a control chamber of variable volume, a constricted passageway connecting the control chamber with the first variable volume space, a transfer passage also in the plunger, the control piston being subjected at one end to the gas pressure in said first variable volume space while its other end is subjected to the gas pressure in the control chamber, a change-over valve which is operated by the control piston and is arranged to connect the transfer passage to either the first or the second variable volume space, depending upon the position of the control piston in the control cylinder, and a dual non-return val e device permitting gas to flow from the first and second variable volume spaces into the transfer passage, but not directly from one of said variable volume spaces to the other.

2 A pneumatic suspension device according to claim 1, in which thechange-over valve comprises a groove around the control piston permanently connected with the transfer passage, and a port which is formed in the control cylinder and leads into the second variable volume space, the groove sliding beyond the control cylinder and thus communicating with the first variable volume space when the control piston is advanced, and communicating with the second variable volume space by way of the port when the control piston is retracted.

3. A pneumatic suspension device according to claim 1, in which the constricted passage comprises a clearance space between the interior of the control cylinder and the outside of the control piston.

4. A pneumatic suspension device according to claim 1, in which the dual non-return valve device comprises a pair of annular side Walls defining a groove around the outside of the piston head, a port leading from the base of said groove into the transfer passage, an annular packing member loosely fitted within said groove with freedom to move axially and seat against either side wall, the packing member engaging at its outer peripheral surface with the wall of the cylinder, while its inner periphery is spaced from the base of the groove.

5. A pneumatic suspension device according to claim 1, in which the dual non-return valve device comprises a cavity in the piston head, an opening connecting said cavity with the transfer passage, opposed seats formed in said cavity leading respectively into the first and second variable volume working spaces, a pair of valve members disposed within said cavity and resilient means urging said valve members into sealing engagement with said seats.

6. A pneumatic suspension device according to claim 1, in which the dual non-return valve device comprises a cavity in the piston head, an opening connecting said cavity with the transfer passage, opposed seats formed in said cavity leading respectively into the first and second variable volume working spaces, a pair of valve members disposed within said cavity and a coiled compression spring engaging at opposite ends with the valve members to urge said valve members apart into resilient engagement with their respective seats.

'7. A pneumatic suspension device according to claim 1, in which the dual non-return valve device is carried upon the control piston and comprises a head member fast upon the control piston and having a pair of opposite end faces, passages extending through the head member from one end face to the other, and a pair of annular valve members engageable respectively with the tWo end faces to seal the said passages and prevent fiow of gas thereinto.

8. A pneumatic suspension device according to claim 1, in which the dual non-return valve device comprises an axial spigot formed upon the control piston. a head member fast upon saidspigot and having a pair of opposite end faces, passages extending through the head member from one end face to the other, and a pair of annular valve members which are slidable upon the spigot and are engageable respectively with the two end faces to seal the said passages and prevent flow of gas thereinto.

9. In a pneumatic suspension device for vehicles having a cylinder closed at oneend; a

plunger of substantially smaller diameter than the cylinder and slidable therein, packing-means on the end of the cylinder forming a seal against. the plunger, and on the innerend of the plunger, a piston head which slidably engages the interior, of the cylinder, and divides the interior of the cylinder into a first variable volume space bounded by the piston head and the closed end of the cylinder, and a second variable volume space of annular cross section surrounding the plunger, said first and second variable volume spaces both being charged with gas under pressure, the provision of a pneumatic damping valve system comprising a control cylinder formed by a bore extending through the piston head and having an open outer end, a wall closing the inner end of the control cylinder, a control piston slidable within the outer end of said control cylinder to form a control chamber of variable volume, a constricted passageway extending through the control piston and connecting the control chamber with the said first variable volume space, a transfer passage in the plunger, a change-over valve which is operated by the control piston and is arranged to connect the transfer passage to either the first or the second variable volume space, depending upon the position of the control piston in the control cylinder, and a dual nonreturn valve device permitting gas to flow from the first and second variable volume spaces into the transfer passage, but not directly from one oi said. variable volume. spaces-to. the other.

1.0.. In a pneumatic suspension device for vehilcles having a cylinder closed atv one end, a plunger of substantially smaller diameter than the cylinder and slidable therein, packing means on the end of. the cylinder forming a seat against the plunger, and on. theinner endof the plunger a piston head which slidably engages the interior of. the cylinder, andv divides the interior. of the cylinder into a first variable volume space bounded by the piston head and the closed end of the cylinder, and a second variable volume space of. annular cross section. surrounding. the plunger, said. first and second variable volume spaces both being, charged with. gas under pressure, the provision of a pneumatic damping valve system, comprising a control cylinder formed by a bore extending through the piston head and having an open outer end, a wall closing the inner end of the control cylinder, 21 control piston slidable within the outer end of said control cylinder. to form a control chamber. of variable volume, a constrictedpassageway extending, through the control piston and connecting the control cham her with the said, first variable volume. space, a tube on the control piston extending from the constricted passageway to a position adjacent the closed. inner end of the control cylinder, a transfer passage in the plunger, a change-over valve which is operated by the control. piston and is arranged to connect the transfer passage to either the first or the second variable volume space, depending upon the position of the control piston in the control cylinder, and a dual non-return valve device permitting gas to flow from the first and second variable volume spaces into the transfer passage, but not directly from one of said variable volume spaces to the other.

11. A pneumatic suspension device according to claim I, in which the change-over valve comprises'a groove around the control piston forming the transfer passage, opposed frusto-conical' sur faces: forming opposite side walls of said groove, and. a pair of opposed seatings on the piston head, both disposed within said groove and having an axial separation less than the distance between said frusto-conical surfaces, whereby axial movement of the control piston causes only one of the frusto conical surfacesto engage with its seating.

L2: A pneumatic suspension device according toclaim; 1, in which the dual non-return valve comprises a cavity formed in the control piston, opposed seats; in said cavity, passages leading. from the cavity by way of said seats into the first and second variable volume working spaces, a permanent connection between the cavity and the transfer passage, an pair 0t valve members disposed within the cavity and normally engaging said opposed seats and resilient means urging said valve members apart into engagement-with said seats.

13.. A pneumatic suspension device. according to claim 1, a circumferential groove. in the control piston, with mutually parallel annular side walls and a stem portion defining the base of the groove, ports formed in saidside walls. and leading into the first and second variable volume working spaces, respectively, a pair of flat annular valve members disposed slidably upon said stem portion, and resilient means urging the valve members apart into seating engagement with the side walls to close the ports formed therein, the annular valve members constituting the dual nonreturn valve device, and the groove cooperating with the piston head to form the change-over valve.

PETER WARBORN THORNHILL.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 1,991,043 Bates Feb. 12, 1935 2,089,657 Mercier Aug. 10, 1937 2,098,398 Mercier Nov. 9, 1937 2,150,390 Mercier Mar. 14, 1939 2,275,462 Parills Mar. 10, 1942 2,393,493 Brown Jan. 22, 1946 FOREIGN PATENTS Number Country Date 509,104 France Augfll, 1920 408,592- Great Britain Apr. 5, 1934' 826,293" France Jan. 4, 1938' 49,470 France J an. 1'7; 193'9' 

